By Kathryn Westcott
The alleged international paedophile ring smashed in Austria highlights the ease with which criminal gangs have been able to exploit the internet to make money out of child abuse.
According to investigators in Austria, some 2,360 suspects from 77 countries downloaded horrific images of young children being sexually abused and raped.
There has been an increase in commercial pornography sites
They were believed to have been shot in Eastern Europe and uploaded to the web in Britain, posted on a Russian website hosted by an Austrian company.
Investigators say that in a 24-hour period they recorded more than 8,000 hits on the site from computer address in countries from America to Algeria and Macedonia to Mexico.
Some of the material was free but the Russian site was charging $89 (68 euros, £45) for access for a "members' only" section.
Experts have described this type of criminal activity as fairly routine. They say there has been a growth in technologically sophisticated pay-per-view sites. The sites are difficult to detect and close down because of the way in which they move around the world.
John Carr, an expert on child pornography and the internet with the UK children's charity NCH, says that in such cases where there is a large commercial element involved, it is often criminal gangs who are producing the images and running the sites.
These gangs have huge databases of paedophiles who are then directed to sites, via e-mails and message boards.
"Images can be uploaded in, say Britain, and then downloaded around the world in minutes or hours, depending on how effective the network is," he says.
The files are difficult to detect. Everything that transverses the internet looks the same while in transit. Traffic gets broken up into packets of data that do not identify what they contain. So an innocuous e-mail looks the same as illegal, pornographic images.
In this case, police got a lucky break after a technician employed by a Vienna-based internet company noticed that a series of violent videos involving children had been downloaded onto his computer.
It appears that criminals had hijacked the computer to hide their trail as they passed the images to Russia.
The technician then informed the police.
Mr Carr told the BBC News website that these kinds of "lucky breaks" were common in cases of internet pornography.
"A large proportion of policing successes in this area is intelligence led. It usually comes from a tip off from a parent or child," he says.
He said it was hard for police to routinely set out to find such files being passed along the internet. "There are 'sniffer' programmes that can look at the data stream. In Britain, however, you have to have a warrant to use them, otherwise this would be surveillance," he says.
Search engines regularly "crawl" the web in search of such illegal material but criminals and paedophiles can cloak salacious keywords inside images, making them harder to detect by the text-based scans.
Gangs have databases of paedophiles they contact via e-mail
Mr Carr says that the gangs move quickly, setting up illegal sites operating for a short period of time and then moving on.
"They know the cops are going to come after them. They know it's not going to last very long. It's smash and grab - they are in and out. They make a lot of money and move on," he says.
Because of its global nature, the internet is a difficult place to regulate. Many of those involved in the fight against internet child pornography argue that a more joined-up approach by international agencies is needed to crack down on criminals.
"You can have a site that is registered to say someone in Britain, which is being operated out of America and posted on networks in Russia," says Sarah Robertson of the Internet Watch Foundation (IWF).
She says that commercial websites are able to avoid detection by hopping from server to server and from one host country network to another.
According to IWF, the US and Russia host the bulk of the world's child abuse sites. It identifies the UK as one of the countries with the best enforcement records.
In a recent report, the organisation said that 51% of child abuse content was traced back to the US and 20% to Russia. This compared with less than 1% of potentially illegal content that appeared to be hosted in Britain.
"The longevity of commercial sites is very worrying," says Ms Robertson. "We've been calling for a more joined up approach to the problem. We're doing a great job in the UK of getting the sites removed once they are detected but in other countries, there is a problem over jurisdiction and who is responsible for taking those sites down."
Some sites, she says, even brag about their longevity.
But, others argue that Operation Flo is an indication that international agencies are beginning to move in the right direction. They argue that the case underlines strong cross-border co-operation to combat online child pornography.
"There are positive messages that come from this case," Jim Gamble of the Child Exploitation and Online Protection Centre told the BBC.
"The UK is one of the most difficult places to host these images. Where people go abroad using proxy servers or access through other sites, they are finding that law enforcement is so joined up they can't hide."